U.S. patent number 3,877,995 [Application Number 05/420,984] was granted by the patent office on 1975-04-15 for potassium borate glass compositions.
This patent grant is currently assigned to The Dow Chemical Company. Invention is credited to Charles A. Levine, Floris Y. Tsang.
United States Patent |
3,877,995 |
Levine , et al. |
April 15, 1975 |
Potassium borate glass compositions
Abstract
An amorphous glass sytem based on potassium borate, which may
also contain additives to modify viscosity, expansion coefficient,
and the like, has found particular utility as the membrane material
in alkali metal-sulfur batteries due to its inertness towards
potassium, sulfur and potassium sulfide, as well as its excellent
ability to conduct potassium ions.
Inventors: |
Levine; Charles A. (Concord,
CA), Tsang; Floris Y. (Concord, CA) |
Assignee: |
The Dow Chemical Company
(Midland, MI)
|
Family
ID: |
26958027 |
Appl.
No.: |
05/420,984 |
Filed: |
December 3, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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276592 |
Jul 31, 1972 |
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Current U.S.
Class: |
429/104; 501/49;
429/321; 501/43 |
Current CPC
Class: |
H01M
50/431 (20210101); H01M 10/3918 (20130101); C03C
3/247 (20130101); H01M 50/489 (20210101); C03C
3/064 (20130101); C03C 4/18 (20130101); H01M
50/44 (20210101); C03C 13/00 (20130101); C03C
3/23 (20130101); C03C 3/14 (20130101); H01M
50/437 (20210101); H01M 2300/0048 (20130101); Y02E
60/10 (20130101) |
Current International
Class: |
C03C
3/064 (20060101); C03C 3/14 (20060101); C03C
4/18 (20060101); C03C 3/062 (20060101); C03C
4/00 (20060101); C03C 3/12 (20060101); C03C
13/00 (20060101); C03C 3/247 (20060101); C03C
3/23 (20060101); H01M 2/16 (20060101); H01M
10/39 (20060101); H01M 10/36 (20060101); H01m
003/02 () |
Field of
Search: |
;136/6FS,153,146
;106/47R,54 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Douglas; Winston A.
Assistant Examiner: Niebling; John F.
Attorney, Agent or Firm: Lochhead; J. Roger
Parent Case Text
This application is a continuation-in-part of my co-pending
application Ser. No. 276,592, filed July 31, 1972, and now
abandoned entitled "POTASSIUM BORATE GLASS COMPOSITIONS".
Claims
1. An amorphous potassium borate glass system of the formula
K.sub.2 O. (2+a) B.sub.2 O.sub.3. (b-c-e) KX. c/2 M(X').sub.2. dY.
e/3 M' (X").sub.3 wherein, in the formula,
-0.5< a< 2;
O< b.ltoreq. (1+a/2) + 0.3, when X is F;
O< b.ltoreq. (1+a/6) + 0.1, when X is Cl or Br;
O.ltoreq. c.ltoreq. b;
O.ltoreq. d.ltoreq. 1;
O.ltoreq. e.ltoreq. (b-c);
M is Mg, Ca, Sr or Ba;
M' is Al or Ga;
Y is SiO.sub.2 or 1/2 R.sub.2 O.sub.5 ; and
2. The composition of claim 1 wherein, in the formula,
O.ltoreq. a.ltoreq. 0.2,
0.01.ltoreq. b.ltoreq. 0.5,
O.ltoreq. c.ltoreq. 0.2,
3. In a battery cell comprising a first oxidizable liquid metal
electrode,a second fluid reducible electrode and a substantially
fluid tight membrane separating said first and second electrodes,
the improvement which comprises a separating membrane fabricated
from an amorphous potassium borate glass composition of the
formula
K.sub.2 o. (2+a) B.sub.2 O.sub.3. (b-c-e) KX. c/2 M(X').sub.2. dY.
e/3 M'(X").sub.3 wherein, in the formula,
-0.5< a< 2;
O.ltoreq. b.ltoreq. (1+a/2) + 0.3, when X is F;
O.ltoreq. b.ltoreq. (1+a/6) + 0.1, when X is Cl or Br;
O.ltoreq. c.ltoreq. b;
O.ltoreq. b.ltoreq. 1;
O.ltoreq. e.ltoreq. (b-c);
M is Mg, Ca, Sr or Ba;
M' is Al or Ga;
Y is SiO.sub.2 or 1/2 P.sub.2 O.sub.5 ; and
4. The article of claim 3 wherein, in the formula,
O.ltoreq. a.ltoreq. 0.2,
0.01.ltoreq. b.ltoreq. 0.5,
O.ltoreq. c.ltoreq. 0.2,
5. The article of claim 3 wherein the separating membrane is in the
form of one or more fine hollow fibers having an outside
diameter/wall thickness ratio of from about 3 to 20, ranging in
outside diameter from about 20 to 1000 microns and a wall thickness
of from about 5 to 100 microns.
Description
BACKGROUND OF THE INVENTION
A significant development in the area of battery cells,
particularly secondary battery cells (cells which can be discharged
and electrically recharged numerous times without injury to the
cell), has been the introduction of alkali metal-sulfur batteries.
U.S. Pat. Nos. 3,404,035 and 3,476,602 are examples of this new
technology.
This type of cell generally consists of a liquid anode (a melt
consisting of one or more alkali metals, alkali metal amalgams, or
alkali metal alloys); a liquid or paste sulfur cathode (some of
which is melted and in which the cations of the metal are
dispersed); and an electrolyte-separator or membrane which is
selectively permeable to the cations of the metal and which
separates the anode and cathode. This membrane, is further adapted
to transmit ions of the anode metal between the anode and cathode
compartments without transmitting, to any appreciable extent,
electrons, molecules of the anode metal, or ions or molecular
species of the cathode. The anode, cathode, and membrane elements
are typically positioned within a liquid and vapor tight case.
Electrically-conducting leads are attached to the anode and cathode
to complete the battery unit.
Typically, these batteries have utilized a liquid sodium anode; a
liquid sulfur-sodium sulfide mixture, e.g., a sodium polysulfide,
as the cathode; and a sodium ion conductive glass as the membrane.
As a cathode, sodium sulfide dissolved in, or in admixture with,
sulfur has been discovered to be especially suitable inasmuch as
these two components form mixtures that become liquid at relatively
low temperatures (a minimum temperature between about
270.degree.-330.degree.C.), and which also exhibit unexpectedly
high electrical conductivity over broad ranges of compositions.
We have now discovered that, in a battery cell utilizing a liquid
potassium metal anode and liquid sulfur-potassium sulfur mixtures,
e.g., potassium polysulfide, as the cathode, a potassium
ion-conductive glass membrane is advantageous. Such cells, and
their operation, are described in U.S. Pat. No. 3,476,602.
Electrolyte-separators or membranes suitable for use in these types
of cells, then, must possess the ability to keep the liquid anode
separated from the liquid cathode and they must also be conductive,
i.e., they must possess the ability to transmit ions of the anode
metal between the anode compartment and the cathode compartment but
they sould not, in any substantial way, conduct electrons, the
elemental anode metal or the cathode material in either its
molecular or ionic form. Furthermore, these membranes should resist
degradation during operation, be inert to chemical attack by the
liquid components of the cell and, preferably, should have high
ionic conductivity.
To secure the greatest efficiency and the highest energy density,
the electrolyte-separator is generally utilized in the form of thin
membranes fabricated in various geometries and dimensions. Suitable
membranes include flat plates, corrugated sheets, spirals, hollow
fibers and other shapes designed to provide for ready anode metal
ion transfer during battery operation, but which will keep the
liquid anode and cathode materials separated.
Glasses and porcelain materials have been utilized by the prior art
as such a membrane material. Many silicate systems have been tried,
e.g., K.sub.2 0.4 SiO.sub.2, but have not been proven satisfactory.
It has been found that, depending upon the K.sub.2 OO content, they
are not chemically resistant enough to potassium, sulfur or
sulfide.
While potassium borates are known (see, for instance, Levin et al.,
Phase Diagrams for Ceramists, Diagram No. 165, p. 87, Am. Ceramic
Society (1964) ), there are no reported potassium borate-alkali
halide amorphous glass systems.
DESCRIPTION OF THE INVENTION
The present invention provides an amorphous glass system based on
potassium borate which may also contain additives to modify
viscosity, expansion coefficient and the like.
In one respect, the invention is a glass system which finds
particular utility as a separator membrane in an alkali-sulfur
battery cell, said glass being a potassium borate which may
optionally contain potassium halide and other additives.
In another respect the invention is an amorphous potassium
borate/potassium halide glass system which may contain viscosity
modifiers and the like.
More particularly, the invention is an amorphous potassium borate
glass system of the formula
K.sub.2 o.( 2+a) B.sub.2 O.sub.3.(b-c-e)
KX.(c/2)M(X').sub.2.dY.(e/3)M'(X").sub.3
wherein, in said formula, -0.5 <a<2; O <b.ltoreq.(1+a/2) +
0.3, when X is F, or O <b.ltoreq.(1+a/6) + 0.1, when X is Cl or
Br; O.ltoreq.C.ltoreq.b; O.ltoreq.d.ltoreq.1;
O.ltoreq.e.ltoreq.(b-c); M is mg, Ca, Sr or Ba; M' is Al or Ga; Y
is SiO.sub.2 or 1/2 P.sub.2 O.sub.5 ; and X, X' and X" are,
independently, Cl, Br or F.
The above glass system has been found to be chemically inert toward
potassium, sulfur and potassium sulfide. Further, it demonstrates
reasonably high potassium ion conductance. Therefore, this glass
finds a specific utility as a separator membrane material for
alkali metal-sulfur batteries, particularly when in the form of a
fine, hollow fiber. It has also been found that the above glass
system is suitable for use as a separator membrane when b = O.
For use as the membrane material in an alkali-sulfur battery cell,
preferred ranges for those variables in the above formula are as
follows:
O.ltoreq.a.ltoreq.0.2
0.01.ltoreq.b.ltoreq.0.5
O.ltoreq.c.ltoreq.0.2
d and e = O
M = mg
X and X' = F.
A preferred structure for a separator membrane produced from the
glass of this invention is one or more very fine, hollow fibers
having outside diameter-to-wall thickness ratios of about 3-20 and,
desirably, about 4-10. When these ratios are present, hollow fibers
having an outside diameter of about 20-1000 microns and a wall
thickness of about 5-100 microns are normally employed. Such fibers
can provide a high strength, thin-walled membrane which can promote
a high ion conductivity and supply a very large surface
area-to-volume ratio. Although obviously less advantageous in the
latter respect, hollow fibers having an outside diameter of 5000
microns with wall thicknesses of 1000 microns can be employed but
the efficiency and energy density of the cell is substantially
reduced.
SPECIFIC EMBODIMENTS
Example 1
Stoichiometric amounts of K.sub.2 CO.sub.3, B.sub.2 O.sub.3, and KF
(as needed to prepare K.sub.2 0.3 B.sub.2 03.KF), in powder form,
were weighed out, thoroughly dried and blended together. This
mixture was placed in a platinum dish and the dish and its contents
heated to 900.degree.C. After the mix had completely melted, it was
stirred with a graphite rod, and then poured onto a graphite plate
and allowed to cool rapidly. There resulted a clear, transparent
glass with a softening point of 418.degree.C.
After 5 months at room temperature, the glass was still clear and
transparent, showing little or no tendency to devitrification at
room temperature.
Example 2
Stoichiometric amounts of K.sub.2 CO.sub.3, B.sub.2 O.sub.3 and KF
(as needed to prepare K.sub.2 O. 2.14 B.sub.2 O.sub.3. 0.5 KF),
were weighed out, dried, mixed and melted as in Example 1. When
this glass was poured out onto a graphite plate, a clear,
transparent glass resulted (softening point of
415.degree.-25.degree.C.), although the outer edges did show a
tendency to crystal growth. Most of the glass remained transparent
and no further devitrification took place over a 5-month period at
room temperature.
Example 3
In a manner similar to Examples 1 and 2, the following glasses were
made:
K.sub.2 0.2b.sub.2 o.sub.3.1/6 kf
k.sub.2 0.2b.sub.2 o.sub.3.1/6 kcl
K.sub.2 0.2b.sub.2 o.sub.3.0.4 kf.0.05 mgF.sub.2
K.sub.2 0.2b.sub.2 o.sub.3.0.08 kbr.0.2 SiO.sub.2.
The above were all clear glasses.
Example 4
A melt of K.sub.2 0.2B.sub.2 O.sub.3.0.3 KF.0.1 MgF.sub.2, prepared
as above, was cooled to an appropriate viscosity (about 4 .times.
10.sup.3 poises at 620.degree.C.) and a hollow fiber was hand-drawn
from it by standard glass blowing techniques. The fiber had an
outside diameter of about 400.mu. and an inside diameter of about
220.mu..
A 6-inch section of this fiber was then sealed at one end to form a
suitable glass capillary for use in a lab-scale battery.
The battery was made as follows: A 12-inch length of 5 mil aluminum
wire was inserted into the open end of the glass capillary and the
assembly placed in an inert atmosphere box. The open end of the
capillary was then placed in a pool of liquid potassium held at
150.degree.C. The gas from the inside of the capillary was then
removed by vacuum, and, when the vacuum was released, liquid
potassium filled the capillary. This potassium-filled glass
capillary tube, with the aluminum wire emerging from the open end,
was then inserted, closed-end down, into a 1 cm. diameter test tube
(8 inches long) that contained about 4 gm. of solid K.sub.2
S.sub.4.
A 10 mil stainless wire was inserted into the test tube alongside
the glass capillary, and the two wires were brought out of the test
tube through a rubber stopper. The wire from the potassium was the
anode lead and the wire from the k.sub.2 S.sub.4 was the cathode
lead. The bottom 4 inches of the test tube was then heated and
maintained at 300.degree.C., and a working battery model resulted.
(See U.S. Pat. No. 3,476,602 for further details regarding
construction of such cells).
Measuring the voltage across the anode and cathode leads gave about
2.13 volts. When this cell was discharged by placing a 100 K
resistor across the leads, 18 microamperes of current was drawn.
The terminal voltage showed 1.77 volts. Similarly, when the cell
was charged by providing 18 microamperes charging current, the
terminal voltage was 2.49 volts. Thus, the internal resistance of
the cell was about 20 K.OMEGA..
The cell was intermittently charged and discharged, and then held
at open circuit. Cell constants remained the same after operating
in this manner for 7 weeks.
* * * * *